Refrigerant compressors are used to circulate refrigerant in a chiller via a refrigerant loop. One type of known refrigerant compressor operates at fixed speed and has a set of variable inlet guide vanes arranged at a compressor inlet, upstream from an impeller. The variable inlet guide vanes are actuated during operation of the refrigerant compressor to regulate capacity during various operating conditions.
Other known refrigerant compressors have additionally employed a variable-geometry diffuser downstream from an impeller to improve capacity control during part-load operating conditions. Variable-geometry diffusers adjust the diffuser cross-sectional flow area to the low flow rate encountered under part-load conditions, thus maintaining flow angles and velocities similar to those at full-load design conditions.
One prior refrigerant compressor concept suggested recirculating refrigerant to improve capacity control. In U.S. Pat. No. 5,669,756 to Brasz, for example, the refrigerant is recirculated from a diffuser exit, and is injected back into a main flow path at the impeller.